This invention relates to a method of controlling intake air quantity for internal combustion engines, and more particularly to a method of this kind which is capable of supplying with accuracy a required quantity of supplementary air to the engine when the engine is operating in a particular operating condition at a low atmospheric pressure, such as at a high altitude.
A method of controlling intake air quantity is generally known, which is adapted to supply the engine with supplementary air in quantities responsive to the engine temperature, e.g. the engine cooling water temperature, when the engine is operating in particular operating conditions such as in cranking and warming-up conditions, to thereby ensure stable startability of the engine and prompt completion of the warming-up of the engine.
To carry out the intake air quantity control method mentioned above, a supplementary air quantity control system has been proposed, e.g. by U.S. Pat. No. 4,479,471 issued Oct. 30, 1984, which comprises a fast idling control valve arranged in an auxiliary air passage bypassing the throttle valve and adapted to open and close by means of thermal expansion and contraction of a thermally expandable member responsive to the engine cooling water temperature for regulating the supplementary air quantity, and a solenoid control valve arranged in another auxiliary air passage bypassing the throttle valve and adapted to open with a valve opening duty ratio dependent on the engine cooling water temperature.
According to the proposed method, however, when the engine is operating in a particular operating condition at a low atmospheric pressure such as at a high altitude, there can occur a shortage of supplementary air if the engine is supplied with a quantity of supplementary air which is dependent solely upon the engine temperature and set at a value appropriate to a corresponding particular operating condition at a reference atmospheric pressure, e.g. standard atmospheric pressure, since the mass flow rate of intake air supplied to the engine per suction stroke of same decreases with a decrease in the density of air in a low atmospheric pressure condition. This makes it difficult to achieve desirable startability of the engine and also to maintain the idling speed of the engine at a required value while the engine is idling for warming-up after completion of cranking operation, making the operation of the engine unstable.